Blocking apparatus and method utilizing a low-energy ion beam

ABSTRACT

Apparatus and method for producing a blocking pattern of the crystalline structure of a solid surface using a low-energy ion beam is shown wherein the low-energy ion beam is focused to a predetermined cross section and directed by an extended bored member onto a predetermined area of the solid surface at an angle greater than 5* and less than 90* enabling the ions to be scattered from the solid surface to produce a projected blocking pattern which impinges upon a fluorescent screen positioned substantially parallel to and spaced a predetermined distance from the solid surface for producing as a visual image the projected blocking pattern representing the crystalline structure of the solid surface. The extended bored member also collimates the focused ion beam into a smaller predetermined cross section and produces secondary electrons while collimating the focused beam to thereby produce a cloud of electrons which neutralize any charge at the solid surface produced by incidence of the collimated ion beam.

[72] Inventors David P. Smith 3,277,297 l0/l966 Forrester et al. 250/495(5) Hudson, Wls.; 3,4l5,985 12/1968 Castaing etal. 250/495 (9) JamesS810 Grove Primary Examiner-James W. Lawrence Minn Assistant Examiner-AL Birch [2]] Appl' A K Al I d s 11 s ld & D 1 h Filed Sept. I6, 1968trorneylnney, exan er, e te t e a um [45] Patented Nov.23, 1971 1Assignee Mlnmm Mining and Manufmul'ing ABSTRACT: Apparatus and methodfor producing a blocking p y pattern of the crystalline structure of asolid surface using a st-pauliMlnnlow-energy ion beam is shown whereinthe low-energy ion beam is focused to a predetermined cross section anddirected BLOCKING APPARATUS AND METHOD zyean legtenged bored merlnberonto a; prestietegriined fireagg f;

UTILIZING ALOWENERGY ION BEAM so 1 su ace at an ang e greater t an aness t an enablmg the ions to be scattered from the solid surface to 13Chums 5 Drawing produce a projected blocking pattern which impinges upona [52] U.S.Cl 250/495, fluo escent screen positioned substantiallyparallel to and 2l9/ 121 spaced a predetermined distance from the solidsurface for [51] Int.Cl H0lj 37/26 producing as a visual image theprojected blocking pattern [50] Field of Search 250/495 representing thecrysta line structure of t e so id surface. The (I), 49.5 (5), 49.5 (9);219/121 EB extended bored member also collimates the focused ion beaminto a smaller predetermined cross section and produces Reierences citedsecondary electrons while collimating the focused beam to UNITED STATESPATENTS thereby produce a cloud of electrons which neutralize any3,221,133 1 1/1965 Kazato et al. 250/495 1 charge at Surface Produced byincidence mated ion beam.

BLOCKING APPARATUS AND METHOD UTILIZING A LOW-ENERGY ION BEAM Low-energyion scattering apparatus and method are known in the art. Such apparatusand methods are described in an article entitled The Influence ofAbsorbed Gases On Surface Analysis For Low-Energy Ion Scattering" byDavid P. Smith which appeared in the Oct. l966 Transactions of theThirteenth National Vacuum Symposium of the American Vacuum Society atpages I89 and 190 and in an article entitled Scattering of Low-EnergyNoble Gas Ions From Metal Surfaces" by David P. Smith which appeared inthe Jan. 1967 Journal of Applied Physics at pages 340-347.

The above-noted articles clearly and sufiiciently describe the use oflow-energy ion scattering wherein the energy of a scattered primary gasion is used for surface compositional analysis of a solid surface.

In a recent article entitled Proton Scattering Microscopy" by R. S.Nelson which appeared in the Apr. 1967 Philosophical Mag, Volume l5 atpages 845-854, a method and apparatus are disclosed for producing whatNelson considers to be proton blocking patterns on a fluorescent screenusing protons having an energy in excess of Kev.

The use of high-energy proton beams having energies in the i order of 20Kev. for producing proton blocking patterns to represent the atomicstructure of a crystalline surface have several inherent disadvantages.For example, the use of highenergy protons extracted from conventionalplasma-type sources and utilized to produce a blocking patternrepresenting the crystal structure of the surface of an insulatingmaterial causes the insulating material to store a charge thereon whichhas the effect of establishing a field which repels the proton beambeing directed onto the surface thereof.

- Other disadvantages of the prior 'art apparatus include that a massanalyzer must be used to obtain an ion beam of desired mass and energyand that the apparatus must operate at high voltage levels in the orderof 20 kv. or higher. In addition, when samples to be analyzed are of aninsulating material, it appears that the sample builds up a positivesurface charge which may repel the ion beam. Also, the samples must beseparately cleaned and prepared by separate apparatus and methods foruse before the solid surface thereof can be analyzed by the priorapparatus.

The present invention overcomes the disadvantages of the prior artapparatus and method for analysis of the crystalline structure of thesurface of material by use of a unique and unusual means for directingan ion beam onto the surface of the material. The ion beam directingmeans includes an extended bored member which is capable of collimatinga focused ion beam of a predetermined cross section into a collimatedion beam of a smaller predetermined cross section, of directing thecollimated ion beam to a predetermined area of the material surface, andof producing secondary electrons while collimating the ion beam toproduce a cloud of electrons which are attracted to the material surfaceto prevent a sur face charge built up on the surface of the materialwhich otherwise would repel or interfere with the ion beam beingdirected upon the material surface. The neutralizing capability isparticularly significant when producing a blocking pattern from aninsulating material.

Another advantage of the present invention is that lowenergy ions havingan energy level in the order of less than l0 Kev. can be used forproducing the ion blocking pattern illustrating the atomic structure ofa solid surface.

Another advantage of the present invention is that an ion beamgenerating source is disclosed which is capable of precisely directingan ion beam of a predetermined cross section onto a predetermined areaof a solid surface which is to have an ion blocking pattern producedillustrating the crystal structure of the solid surface.

Yet another advantage of the present invention is that a unique andnovel method for generating an ion blocking pattern representing thecrystalline structure of a solid surface by use of low-energy ionsscattered from the surface is disclosed.

Still another advantage of the present invention is that in a preferredembodiment one ion beam including both scattering ions and sputteringions can be used for producing a blocking pattern of the solid surfacebeing analyzed and for sputtering or eroding the solid surface at acontrolled rate. The inclusion of both sputtering and scattering ions inthe ion beam has the advantage of providing a convenient means forpreparing a surface by sputtering to remove the atoms of any amorphousor foreign material from the solid surface to be analyzed while thesample is mounted for observation by the scattering ion in the beam.

These and other advantages become readily apparent in light of thedetailed description of the preferred embodiment disclosed herein takentogether with the drawing wherein:

FIG. I is a frontal cross-sectional view of an ion generating sourcecapable of producing low-energy ion beams having a predetermined crosssection;

FIG. 2 is a pictorial representation illustrating the relationshipbetween the end of the ion source relative to a solid surface which isto have a projected blocking pattern of its crystalline structureproduced on a substantially parallel and fluorescent screen spaced at apredetermined distance from the solid surface;

FIG. 3 is a frontal sectional view of a portion of apparatus forselectively positioning a selected one of a plurality of samplesadjacent an ion source for generating a visual blocking pattern whichcan be observed by means of a window;

FIG. 4 is a graphic representation of a blocking pattern of thecrystalline structure of a gold crystal produced by a lowenergy ion beamdirected at and scattered from the surface thereof; and

FIG. 5 is a schematic diagram partially in block form illustrating acontrol system for automatic control of the operation of the apparatusof FIG. 3.

Briefly, the apparatus and method disclosed herein is capable ofproducing a blocking pattern ofa solid surface ofa sample by means of alow-energy ion beam. In one embodiment. the apparatus includes a meansfor generating a low-energy ion beam having a predetermined mass andenergy. A means which cooperates with the generating means is utilizedfor focusing the ion beam into a predetermined cross section. Adirecting means is operatively coupled with the focusing means andcollimates the ion beam into a smaller predetermined cross section. Thedirecting means also directs the collimated ion beam at an angle greaterthan about 5 and less than about onto a predetermined area of the solidsurface enabling the ions to slightly penetrate the solid surface and bescattered from the solid surface as a function of the crystal structureof the atoms forming said solid surface to produce a blocking patternrepresenting as a projected pattern the crystalline structure of thesolid surface and formed of scattered ions from the smallerpredetermined cross-section ion beam. A fluorescent means is positionedsubstantially parallel to and spaced a predetermined distance from thesolid surface. The fluorescent means receives ions scattered from thesmaller predetermined cross-section ion beam forming the blockingpattern for producing as a visual image the blocking pattern whichrepresents as a blocking pattern the crystalline structure of the atomsforming the solid surface.

FIG. 1 illustrates a novel and unique ion source which includes acollimating member having an extended aperture. An ion source support,generally designated as 10, formed of a conductive material is utilizedfor supporting the ion source, generally designated as 12, ion focusingmeans, generally designated as I4, and an ion directing means, generallydesignated as 16. The directing means 16 forms the collimating memberhaving an extended aperture. which in this embodiment is an extendedbore 100. The support 10 is grounded to a common conductor, generallydesignated as 20.

The ion source 12 includes a heatable metallic filament 22 which in thepreferred embodiment is formed of a thoriated tungsten wire. The wirefilament 22 is supported by filament supports 24 and 26 which areisolated from the conductive support by means of insulators 28 and 30respectively. The filament supports 24 and 26 are formed of a conductivematerial and are operatively coupled to the secondary winding of afilament isolation transformer, generally designated as 32. The filamentisolation transformer 32 is in turn energized from a power source whichmay be a variac transformer, generally designated as 34, operativelycoupled to a source of alternating current potential (not shown).

A first or scattering gas source 36 and a second or sputtering gassource 38 are operatively coupled via a first valve 40 and a secondvalve 42 respectively to a tube 43. Tube 43 in turn is connected into anenclosed housing, generally designated as 44, which defines a chamber 46enclosing the wire filament 22. The tube 43 is supported as it passesthrough the support 10 by means of a ceramic insulator 48. The housing44 defining the chamber 46 is mounted on support 10 by means of a raisedcylindrically shaped support 50 which is integral with the planarportion of the support 10. Ceramic spacers 52 are used as supportsbetween the raised cylindrically shaped support 50 and a conductiveshield and support member 54 having raised outer edges 56. The shieldmember 54 is in turn operatively connected to the housing 44 therebyproviding a rigid support for the housing and preventing light emanatingfrom the filament 22 from passing outside of the ionsource.

The housing 44, which defines the chamber 46, terminates in anannular-shaped opening 60. lnterposed between the wire filament 22 andthe opening 60 is a conductive wire mesh 62 which in this embodiment isselected to be tungsten mesh.

ions which are to be scattered from the solid surface of a sample to beanalyzed are generated within the chamber 46 by establishing a potentialdifference between the wire filament 22 and wire mesh 62 to produce alocalized source of electrons and by opening valve 40 and closing valve42 to pass gas from the scattering gas source 36 via tube 43 into thechamber 46 and in the vicinity of the heated wire filament 22. The gasmolecules are bombarded by and interact with the electrons passingbetween the filament 22 and wire mesh 62 to produce the gas ions. Theresulting gas ions pass through the conductive mesh 62 and exit throughthe opening 60 of housing 44.

In the preferred embodiment, the scattering gas is hydrogen. When thehydrogen gas molecules are bombarded by the electrons from filament 22,several ions are produced; namely 'H,', which is an atomic ion, and Hwhich is a molecular ion.

It appears that about equal quantities of each ion are produced.Therefore, mass analysis of the ions is unnecessary and the resolutionof the ion blocking pattern is not seriously affected by the patternsproduced by scattering of each type ion. Also, heavier gas atoms couldbe used as the scattering ion source, such as for example helium, wherehydrogen atoms upon being ionized forming ions would be detrimental dueto chemical reactivity with the surface being analyzed.

if desired, the second or sputtering gas source 38 can be used eitheralternately or simultaneously with the scattering gas source to cleanthe surface being analyzed. Typically, an

inert gas is used for sputtering, such as for example argon. Thesputtering gas can be passed from gas source 38 into chamber 46 via tube43 by opening valve 42. The resulting sputtering gas beam passes alongthe same path as the scattering ion beam.

By using the teachings of the present invention, it is possible toobserve the crystal structure of the solid surface while the same isbeing sputtered or cleaned. This is accomplished by opening both valves40 and 42. Such a feature has wide utility in that a crystalline samplewith a contaminated or amorphous surface layer can be placed into theion blocking apparatus, be sputtered and then have its crystallinestructure displayed. Also, by using the scattering gas source andsputtering gas source concurrently, one can observe the crystalstructure of the solid surface being developed due to cleaning duringthe sputtering process. By knowing ion current densities, sputteringyields and sputtering times required to produce a blocking patternrepresentative of a crystalline surface, it is possible to measure ordetermine the thickness of the amorphous or noncrystalline layer. Thistechnique would have wide utility, such as, for example, to measure thethickness of destruction layers produced by mechanically polishing ofsemiconductor crystals for use in an electron beam laser.

The focusing means 14 is formed of a plurality of spaced parallelannular-shaped lens elements 70-78. Each of the annular-shaped lenselements 70-78 has an opening of predetermined diameter, namely the ionsemanating from opening 60 to pass therethrough. The elements 70-78 arestacked in a coaxial aligned relationship and are spaced from each otherby means of a plurality of insulating spacers, generally designated as80. The combination of annular-shaped members having an aperturetherethrough positioned in aligned coaxial relationship and which forman electrostatic focusing means is generally known as an Einzel focusinglens. As is readily apparent, the diameter of the apertures in each ofthe lens elemerits or plates is selected so that the beam can be focusedto a predetermined cross section at the opening of the last apertureplate 78.

In the embodiment illustrated in FIG. 1, aperture plate 74 iselectrically connected to a variable voltage dividing network, generallydesignated as 84, so that an appropriate focusing potential can beapplied to the ions to form the same into an ion beam. The otheraperture plates 70, 72, 76 and 78 are electrically connected to thecommon conductor 20. A high voltage source, generally designated as 86,is operatively connected to the voltage dividing network 84 which is inturn connected to conductor 20 for providing the desired high voltagefocusing potential. Typically, the high voltage source 86 will provide avariable high voltage output in the order of 0-1 0 kv.

A second lower voltage source, generally designated as 88, isoperatively connected between the housing 44 and one of the filamentsupports 26. The high voltage source 88 is used to control the amount ofbias applied to the wire filament 22.

In the preferred embodiment, the aperture plate 74 is formed ofstainless steel having a thickness in the order of about one-half inch(about 12 mm.) while the other aperture plates 70, 72, 76 and 78 areformed of stainless steel having a diameter in the order of aboutone-quarter inch (about 6 mm). The spaces between each of the apertureplates 70-78 are selected to be about three-fourths inch (about l8 mm).The voltage dividing network 84 is formed of four 4.7-- megohm resistorsand a potentiometer having a rating of 5 megohms. The voltage source 88is selected to have a voltage in the order of to I50 volts DC. The highvoltage source 86 is selected to be in the order of 5 kv. However, insome experiments, a voltage in the order of l kv. was operative.

At the outlet of the focusing means 14 is mounted the directing means 16or collimating member having an extended aperture which in the preferredembodiment is in the form of an extended bored member 100. The boredmember 100 is attached to the aperture plate 78 in alignment with theaxis thereof. The bored member 100 may be formed of a stainless steelneedle having an inside diameter in the order of about .030 inch-(about.75 mm). It is contemplated that a conductive material, which includessemiconductive material, can be used as the directing means. If desired,an insulating material can be used as the directing means, such as, forexample. a thin layer ofaluminum oxide on an aluminum surface.

In this manner, the focusing means 14 can focus the ions emanating fromopening 60 of housing 44 into an ion beam of predetermined cross sectionat a focal point located on the outer surface of annular plate 78 and inalignment with the aperture thereof. The ion beam of predetermined crosssection then passes through the bored member 100 and is collimated intoan ion beam having a cross section which is precisely determined by theinside cross section of the bored member 100.

it has been determined that the outer portion of the ion beam contactsthe inner surface of the bored member 100 and results in the creation ofsecondary electrons which in turn build up a space charge of electronsnear the outlet of bored member 100. The so-generated space charges areattracted to any positive surface charges located on the surface of thesample being bombarded. By this technique, the space charges ofelectrons neutralize the positive surface charges enabling the ion beamto bombard the surface of the sample and be scattered from the surfaceof the sample without the ion beam being repelled or deflected.

FIG. 2 pictorially represents the end of the bored member 100 positionedadjacent a crystalline surface 110 which is mounted onto a support 112.The ion beam, generally designated by line 114, emanates from the outletof bored member 100 which is positioned just adjacent the surface ofsolid 110. The ion beam 114 is directed at a predetermined anglerelative to the surface of the support 112. It has been determined thatthe angle 6 should be greater than and less than 90 such that the ionsfrom the ion beam 114 are scattered into a pattern, generally designatedas 116. During scattering, some of the scattered ions are neutralized bythe electrons in the sample. The scattered ions and other particlesincluding the neutralized ions or atoms bombard a fluorescent means 120which converts the ion blocking pattern into a visual ion blockingpattern. The fluorescent means 120 may be a fluorescent screen 120 whichis positioned substantially parallel to and spaced a predetermineddistance from the solid surface 110.

- When a post accelerating negative voltage was applied to thefluorescent phosphor screen to accelerate positive scattered ions, nodetectable increase in brightness of the fluorescent phosphor wasobserved as would be expected if the scattered ions were not efficientlyneutralized. Thus, it appears that the blocking pattern is formedsubstantially of neutralized ions which, of course, is a blockingpattern formed of scattered ions from the smaller predetermined crosssection ion beam.

The so-produced visual ion blocking pattern is a projected image of thecrystallographic directions in the bombarded sample. The prominent darkareas of the visual ion blocking pattern represent the directions ofrows of atoms in the crystal which inhibit scattering of ions.

The angle limits of greater than 5 and less than 90 set forth above arepractical limits on the angle between the ion beam of smallerpredetermined cross section and the solid surface. Generally, an anglein the order of is preferred.

In the preferred embodiment, the fluorescent screen comprises a thinoptically transparent layer of tin oxide deposited on Pyrex glass andwhich is coated with a uniform thin layer of PI type phosphor. Thepredetermined distance between the fluorescent screen 120 and thesupport 112 is in the order of one-fourth inch to 1 inch (about 6 mm. tomm).

FIG. 3, illustrates an apparatus adapted for producing an ion blockingpattern of the crystalline structure of a solid surface.

The apparatus includes a vacuum chamber, generally designated as 200,which includes an ion gun chamber 204 and a sample support chamber 206.The ion gun chamber 204 is positioned at a predetermined angle relativeto the sample support chamber 206 such that the ion beam can be directedat a predetermined angle onto the surface of the solid which is to havethe ion blocking pattern of its crystal structure produced on afluorescent screen. A support 208 bearing a disk-shaped sample holder210 provides a means for positioning any one of several samples andmaterials for bombardment by the ion beam for generating the ionblocking patterns of the atomic structure of its surface. The supportshaft 212 extends to theoutside of vacuum chamber 200 and is capable ofrotatihg the sample holder 210. A geared positioning member 214 ismounted in a support 215 having a plurality of openings therein. Thegeared positioning member 214 is operatively attached to rotatable shaft226 and is capable of being rotated to position screen support 232 apredetermined distance relative to the sample holder 210. Rotatableshaft 226 extends to the outside of the apparatus so that it can berotated.

A fluorescent screen 230 is supported by a screen support 232 apredetermined distance from the sample holder 210. By rotating shaft226, this distance can be selectively changed to vary the magnificationof the blocking pattern. A window 236 is located on the exterior portionof vacuum chamber 200 in alignment with the fluorescent screen 230 andthe disk-shaped member 210. The window 236 enables a viewer to observethe ion blocking pattern formed on the fluorescent screen 230 when theion beam from the bored member 220 is scattered from the surface of asample located on the sample support 208. The sample support vacuumchamber 206 is evacuated via a pumping port 217 and support 215 to apressure in the order of 10' Torr during operation. Samples within thepumped vacuum of the sample support chamber 206 can be selectivelypositioned by rotating the sample support shafts 212 and 226 therebyenabling a viewer to observe ion blocking patterns from a plurality ofsamples without interruption of the vacuum. Samples can be removed andplaced onto the sample support 208 by admitting atmospheric pressureinto the sample support chamber 206 and by removing a cover 238 which islocated in alignment with the ion gun chamber 204. After the sampleshave been positioned onto the sample support 208, the cover 238 can berepositioned onto the sample support chamber 206 and the entire chambercan then be repumped to the desired vacuum level and operation of theapparatus reestablished.

FIG. 4 illustrates a typical ion blocking pattern produced from a singlecrystal gold surface. The pattern is formed by the ions from thescattering gas source penetrating a few atomic layers into the solidsurface and being scattered back out of the solid. Depending on thecrystalline structure of the sample, which for gold is face centeredcubic, the rows of atoms block or interrupt some of the scattered ionsin a manner analogous to an object interrupting a light beam to producea shadow. This results in the scattered ions, neutralized ions and otherparticles being scattered in a pattern of varying density wherein someof the particles are blocked. Thus, the scattered particles impingefluorescent screen 230 which results in a visual pattern which is aprojection of the crystalline structure of the sample.

If desired, the visual ion blocking pattern can be used as a means foridentifying crystalline surfaces. For example, it is possible to utilizea computer to determine calculated ion blocking patterns by means of amathematical model. Known output devices can be used to plot thecalculated ion blocking pattern. By comparing the calculated ionblocking pattern to the observed ion blocking patterns, a crystallineidentification process or technique can be obtained.

If the sample to be observed on the fluorescent screen 230 of theapparatus of FIG. 3 is an insulating material, the secondary electronsproduced in bored member are accelerated to any positive surface chargeon the insulating surface to eliminate the build up of positive surfacecharge on the insulating material. By reducing the build up of positivesurface charges, the low-energy ion beam is not repelled by charges onthe surface of the insulating material and thereby permits ions toscatter from the surface of the insulating material and to produce anion blocking pattern of the atomic structure of the insulating materialon the fluorescent screen 230. This clearly is an unexpected and novelresult in that the patterns produced by scattering of low-energy ionsare not a function of electrical conductivity of the samples.

FIG. 5. is a schematic diagram illustrating control circuitry forautomatic operation of the apparatus of FIG. 3. The apparatus isenergized from a conventional alternating current source by means ofaplug member 300 which when energized from the alternating current sourceand when a main switch 302 is in its ON position energizes a masterrelay 304. Relay 304 energizes a cooling fan 306 and a main controlrelay 308. The control relay 308 in turn is operatively coupled tovacuum gauges located within the sample support chamber 206 and performsthe function of automatically controlling the vacuum pumping within thesample support vacuum chamber 206 to obtain the desired vacuum in theorder of l Torr. The control relay 308 controls in a predeterminedsequence operation of various valves as the desired vacuum is obtainedin the sample support vacuum chamber 206. Also, if it is desired to ventthe sample support vacuum chamber 206 to atmosphere for addition ofvarious samples, the control relay 308 selectively controls the rate atwhich venting occurs by means of relays, generally designated as 312.Vacuum and pressure indications are displayed on the control panel ofthe apparatus of FIG. 3 by indicating means 314. The portion of thecycle for both pumping the vacuum and venting of the vacuum is indicatedby a cycle indicator, generally designated as 316. ln this manner, theentire operation as to pumping the sample support chamber 206 to anappropriate vacuum and the venting thereof to permit easy and quickinsertion of the samples for subsequent generation of its ion blockingpattern is completely under control of the automatic vacuum circuit. inthis manner, misoperation or interruption of the operation during thetime the vacuum is ON can be precisely controlled.

In addition to the aforementioned embodiment in which the blockingpattern is sensed by viewing the projected pattern produced by scatteredions impinging a fluorescent means, another means of sensing thispattern may be employed with this invention. For example, a screen arraywhich channels secondary emission of electrons upon bombardment of ionsand other particles can be positioned to be impinged upon by thescattered ions. Used with the said aforementioned embodiment, the arraycan be positioned between the solid surface 110 and the fluorescentmeans 120. Such=a screen array is described in the articles The ChannelElectron Multiplier, A New Radiation Detector," by J. Adams and B. W.Manley, which appeared in the 1967 Philips Technical Review, Vol. 28,page 156, and Electron Multipliers Utilizing Continuous Strip Surfaces,"by W. C. Wiley and C. F. Hendee, which appeared in the 1962 Proceedingsof the IEEE, Transaction of Nuclear Science, Vol. 9, page 103. With thisscreen array so positioned, the blocking pattern defined by thescattered ions impinging thereupon can be transformed into an electronemission defining the blocking pattern. Such secondary electrons canthen be accelerated to impinge a fluorescent means. Upon such electronemission impinging the fluorescent means, the blocking pattern can bevisualized.

By interposing such a screen array between the sample from which ionsare scattered and the fluorescent means, there can be also providedmeans which appreciably retard the relatively rapid deterioration of thefluorescent means caused by impingement of the ions and like particlesconveying the intelligence to be discerned and to retard contaminationof the fluorescent means by deposition of atoms sputtered thereon.

This screen array can be prepared to impart a high gain to the intensityof the bombardment, thereby providing a sensing means of highersensitivity. As a result, a lower primary ion current density beam canbe used to scatter the ions from the sample.

Another alternative embodiment for sensing the ion blocking patterncomprises scanning the projected pattern with a single channel electronmultiplier. The output signal from such scanning means can be fed into asuitable display device such as a recorder or an oscilloscope.

We claim:

1. Apparatus for producing a blocking pattern of a solid surface of asample by means of a low-energy ion beam compriss generating means forgenerating a low-energy ion beam having a predetermined mass and energy;

focusing means cooperating with said generating means for focusing saidgenerated ion beam into a predetermined cross section;

directing means including an extended bored member operatively coupledwith said focusing means for collimating said focused ion beam into asmaller predetermined cross section and directing said collimated ionbeam at an angle greater than about 5 and less than about onto apredetermined area of said solid surface enabling said ions to slightlypenetrate said solid surface and be scattered from said solid surface asa function of the crystal structure of the atoms forming said solidsurface to produce a blocking pattern representing as a projectedpattern the crystalline structure of said solid surface and formed ofscattered ions from said directed smaller predetermined cross sectionion beam, which extended bored member has an inside cross sectioncorresponding to said smaller predetermined cross section, and theinterior of which extended bored member includes material capable ofproducing secondary electrons when the extended bored member iscollimating said focused ion beam to thereby produce a cloud ofelectrons to neutralize any charge at said solid surface produced byincidence of said collimated ion beam; and means for sensing saidblocking pattern.

2. The apparatus of claim 1, wherein the extended bored member includesa converging portion at the entry of said focused ion beam into theextended bored member.

3. The apparatus of claim I, wherein the extended bored member is formedof a needle having an inside cross section corresponding to said smallerpredetermined cross section.

4. The apparatus of claim 1, wherein the extended bored member is formedof a stainless steel needle having an inside cross section correspondingto said smaller predetermined cross section.

5. The apparatus of claim 1, wherein the interior of said extended boredmember comprises a conductive material including semiconductivematerial.

6. The apparatus of claim 1, wherein the interior of said extended boredmember comprises an insulating material.

7. The apparatus of claim 1, further comprising a scattering gas source,to which the generating means is operatively coupled for producing ionsto be focused, directed onto, and scattered from said predetermined areaof said solid surface; and

a sputtering gas source, to which the generating means is operativelycoupled for producing ions to be included in said generated, focused,and directed ion beam for sputtering said predetermined area of saidsolid surface.

8. Apparatus for producing a blocking pattern of a solid surface of asample by means of a low-energy ion beam comprising generating means forgenerating a low-energy ion beam having a predetermined mass and energy;

focusing means cooperating with the generating means for focusing saidgenerated ion beam into a predetermined cross-section;

directing means operatively coupled with the focusing means forcollimating said focused ion beam into a smaller predetermined crosssection and directing said collimated ion beam at an angle greater thanabout 5 and less than about 90 onto a predetermined area of said solidsurface enabling said ions to slightly penetrate said solid surface andbe scattered from said solid surface as a function of the crystalstructure of the atoms forming said solid surface to produce a blockingpattern representing as a projected pattern the crystalline structure ofsaid solid surface and formed of scattered ions from said directedsmaller predetermined cross-section ion beam;

sensing means for sensing said blocking pattern;

a scattering gas source, to which the generating means is operativelycoupled for producing ions to be focused, directed onto, and scatteredfrom said predetermined area of said solid surface; and

a sputtering gas source, to which the generating means is operativelycoupled for producing ions to be included in said generated, focused,and directed ion beam for sputtering said predetermined area of saidsolid surface.

9. The apparatus of claim 8, wherein the first gas source is selected tobe hydrogen or helium and the second gas source is selected to be aninert gas such as argon.

10. The apparatus of claim 8, further comprising means for eitheralternatively or simultaneously operatively coupling the sputtering gassource with the generating means.

11. A method for producing a blocking pattern of a solid surface of asample with a low-energy ion beam comprising the steps of generating alow-energy ion beam having a predetermined mass and energy;

focusing said generated ion beam into a predetermined cross section;directing said focused ion beam with an extended bored member at anangle greater than about and less than about 90 onto a predeterminedarea of said solid surface enabling said ions to slightly penetrate saidsolid surface and be scattered from said solid surface as a function ofthe crystal structure of the atoms forming said solid surface to producea blocking pattern representing as a projected pattern the crystallinestructure of said solid surface and formed of scattered ions from saiddirected ion beam, which directing step includes the steps ofcollimating said focused ion beam with said extended bored member havingan inside cross section corresponding to a smaller predetermined crosssection to collimate said focused ion beam into a smaller predeterminedcross section for direction onto said solid surface, and

producing secondary electrons with the extended bored member when theextended bored member is collimating said focused ion beam to therebyproduce a cloud of electrons to neutralize any charge at said solidsurface produced by incidence of said collimated ion beam; and sensingsaid blocking pattern.

12. A method according to claim 11, further comprising the steps ofproviding a scattering gas for producing ions to be focused, directedonto, and scattered from said predetermined area ofsaid solid surface;and

providing a sputtering gas for producing ions to be included in saidgenerated, focused, and directed ion beam for sputtering saidpredetermined area of said solid surface.

13. A method for producing a blocking pattern of a solid surface of asample with a low-energy ion beam, comprising the steps of generating alow-energy ion beam having a predetermined mass and energy;

focusing said generated ion beam into cross section;

directing and collimating said focused ion beam into a smallerpredetermined cross section and at an angle greater than about 5 andless than about onto a predetermined area of said solid surface enablingsaid ions to slightly penetrate said solid surface and be scattered fromsaid solid surface as a function of the crystal structure of the atomsforming said solid surface to produce a blocking pattern representing asa projected pattern the crystalline structure of said solid surface andformed of scattered ions from said directed and collimated smallerpredetermined cross-section ion beam; and

sensing said blocking pattern; wherein the method further includes thesteps of providing a scattering gas for producing ions to be focused,directed onto, and scattered from said predetermined area of said solidsurface; and

providing a sputtering gas for producing ions to be included in saidgenerated, focused, and directed ion beam for sputtering saidpredetermined area of said solid surface.

4: w n r a:

a predetermined UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3 ,7 Dated November 3 1971 Inventor) David P. Smith and Jamesw. Salo It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 2, lines 10 and 11, change "ion in the beam" to ions in the ionbeam I I Column 6, line 13, change "10 7E to l0 Column 7, line 1, change"10 7E to 10 5 Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTISCHALK Attesting Officer Commissionerof Patents RM PO-1 (10-69] USCOMM-DC wave-ps9

1. Apparatus for producing a blocking pattern of a solid surface of asample by means of a low-energy ion beam comprising generating means forgenerating a low-energy ion beam having a predetermined mass and energy;focusing means cooperating with said generating means for focusing saidgenerated ion beam into a predetermined cross section; directing meansincluding an extended bored member operatively coupled with saidfocusing means for collimating said focused ion beam into a smallerpredetermined cross-section and directing said collimated ion beam at anangle greater than about 5* and less than about 90* onto a predeterminedarea of said solid surface enabling said ions to slightly penetrate saidsolid surface and be scattered from said solid surface as a function ofthe crystal structure of the atoms forming said solid surface to producea blocking pattern representing as a projected pattern the crystallinestructure of said solid surfaCe and formed of scattered ions from saiddirected smaller predetermined cross-section ion beam, which extendedbored member has an inside cross-section corresponding to said smallerpredetermined cross-section, and the interior of which extended boredmember includes material capable of producing secondary electrons whenthe extended bored member is collimating said focused ion beam tothereby produce a cloud of electrons to neutralize any charge at saidsolid surface produced by incidence of said collimated ion beam; andmeans for sensing said blocking pattern.
 2. The apparatus of claim 1,wherein the extended bored member includes a converging portion at theentry of said focused ion beam into the extended bored member.
 3. Theapparatus of claim 1, wherein the extended bored member is formed of aneedle having an inside cross-section corresponding to said smallerpredetermined cross-section.
 4. The apparatus of claim 1, wherein theextended bored member is formed of a stainless steel needle having aninside cross-section corresponding to said smaller predeterminedcross-section.
 5. The apparatus of claim 1, wherein the interior of saidextended bored member comprises a conductive material includingsemiconductive material.
 6. The apparatus of claim 1, wherein theinterior of said extended bored member comprises an insulating material.7. The apparatus of claim 1, further comprising a scattering gas source,to which the generating means is operatively coupled for producing ionsto be focused, directed onto, and scattered from said predetermined areaof said solid surface; and a sputtering gas source, to which thegenerating means is operatively coupled for producing ions to beincluded in said generated, focused, and directed ion beam forsputtering said predetermined area of said solid surface.
 8. Apparatusfor producing a blocking pattern of a solid surface of a sample by meansof a low-energy ion beam comprising generating means for generating alow-energy ion beam having a predetermined mass and energy; focusingmeans cooperating with the generating means for focusing said generatedion beam into a predetermined cross-section; directing means operativelycoupled with the focusing means for collimating said focused ion beaminto a smaller predetermined cross-section and directing said collimatedion beam at an angle greater than about 5* and less than about 90* ontoa predetermined area of said solid surface enabling said ions toslightly penetrate said solid surface and be scattered from said solidsurface as a function of the crystal structure of the atoms forming saidsolid surface to produce a blocking pattern representing as a projectedpattern the crystalline structure of said solid surface and formed ofscattered ions from said directed smaller predetermined cross-sectionion beam; sensing means for sensing said blocking pattern; a scatteringgas source, to which the generating means is operatively coupled forproducing ions to be focused, directed onto, and scattered from saidpredetermined area of said solid surface; and a sputtering gas source,to which the generating means is operatively coupled for producing ionsto be included in said generated, focused, and directed ion beam forsputtering said predetermined area of said solid surface.
 9. Theapparatus of claim 8, wherein the first gas source is selected to behydrogen or helium and the second gas source is selected to be an inertgas such as argon.
 10. The apparatus of claim 8, further comprisingmeans for either alternatively or simultaneously operatively couplingthe sputtering gas source with the generating means.
 11. A method forproducing a blocking pattern of a solid surface of a sample with alow-energy ion beam comprising the steps of generating a low-energy ionbeam having a predetermined mass and energy; focusing said generated ionbeam into a predetermined cross-section; directIng said focused ion beamwith an extended bored member at an angle greater than about 5* and lessthan about 90* onto a predetermined area of said solid surface enablingsaid ions to slightly penetrate said solid surface and be scattered fromsaid solid surface as a function of the crystal structure of the atomsforming said solid surface to produce a blocking pattern representing asa projected pattern the crystalline structure of said solid surface andformed of scattered ions from said directed ion beam, which directingstep includes the steps of collimating said focused ion beam with saidextended bored member having an inside cross-section corresponding to asmaller predetermined cross-section to collimate said focused ion beaminto a smaller predetermined cross-section for direction onto said solidsurface, and producing secondary electrons with the extended boredmember when the extended bored member is collimating said focused ionbeam to thereby produce a cloud of electrons to neutralize any charge atsaid solid surface produced by incidence of said collimated ion beam;and sensing said blocking pattern.
 12. A method according to claim 11,further comprising the steps of providing a scattering gas for producingions to be focused, directed onto, and scattered from said predeterminedarea of said solid surface; and providing a sputtering gas for producingions to be included in said generated, focused, and directed ion beamfor sputtering said predetermined area of said solid surface.
 13. Amethod for producing a blocking pattern of a solid surface of a samplewith a low-energy ion beam, comprising the steps of generating alow-energy ion beam having a predetermined mass and energy; focusingsaid generated ion beam into a predetermined cross-section; directingand collimating said focused ion beam into a smaller predeterminedcross-section and at an angle greater than about 5* and less than about90* onto a predetermined area of said solid surface enabling said ionsto slightly penetrate said solid surface and be scattered from saidsolid surface as a function of the crystal structure of the atomsforming said solid surface to produce a blocking pattern representing asa projected pattern the crystalline structure of said solid surface andformed of scattered ions from said directed and collimated smallerpredetermined cross-section ion beam; and sensing said blocking pattern;wherein the method further includes the steps of providing a scatteringgas for producing ions to be focused, directed onto, and scattered fromsaid predetermined area of said solid surface; and providing asputtering gas for producing ions to be included in said generated,focused, and directed ion beam for sputtering said predetermined area ofsaid solid surface.